Development of the in-situ cosmogenic 14C method for studying geomorphic processes

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This research will complete the development of an experimental method for measuring in situ cosmogenic 14C (half-life=5730 yrs) in common surficial terrestrial materials, and for making pilot studies of the method for investigating a few challenging geomorphic problems. From the work carried out to date under NSF grant, we have in hand an experimental method, potentially capable of providing accurate and contamination-free (from environmental 14C) measurements of 14C concentrations. Instead of the commonly adopted method of high temperature fusion, we developed a wet in vacuo method to determine the in situ 14C concentrations in the CO and CO2 phases in the mineral quartz. Environmental 14C does not affect the 14CO measurements, but appears erratically as contamination in the 14CO2 measurement. Since more than 60% of in situ 14C appears in the CO phase, it is convenient to assay in situ 14C by measuring its activity in the CO phase. During the first year, work will primarily be directed towards the development of a robust experimental technique to accurately measure in situ 14C concentration at levels of x104 atoms 14C/g quartz, and the determination of in situ 14C production rates in quartz at different altitudes and latitudes. The latter is a prerequisite for its applications. In the second year, we propose to make some test applications of the in situ 14C method to a number of selected geomorphic problems. It may appear that little can be done in such challenging problems in just one year but we are able to do this because we have at a suite of diverse geomorphic samples in which in situ cosmogenic 10Be and 26Al studies have made earlier in our group. We believe that among the various in situ radionuclides, 14C should offer the most convenient approach for characterizing geomorphic surfaces, providing a firm basis for decisions for further analyses using other in situ radionuclides, e.g. 36Cl, 26Al and 10Be, and the stable nuclide, 21Ne. We are very anxious to complete the development of the experimental method to reliably measure in situ cosmogenic 14C in surficial samples, and to demonstrate its usefulness in geomorphology. //